Hemofiltration system and method based on monitored patient parameters

ABSTRACT

A multipurpose hemofiltration system and method are disclosed for the removal of fluid and/or soluble waste from the blood of a patient. The system and method are equally applicable to adult, pediatric and neonatal patients. In one embodiment, the system continuously monitors the weight of infusate in a first reservoir and drained fluid in a second reservoir and compares those weights to corresponding predetermined computed weights. When necessary, the pumping rates of the infusate, drained fluid and blood are adjusted in order to achieve a preselected amount of fluid removal from the patient&#39;s blood in a preselected time period. Application of this system and method provide repeatable and highly precise results. Alternatively, predetermined patient parameters can be monitored and the adjustment of pumping rates may be responsive to these monitored parameters. Suitable patient parameters are arterial pressure, central venous pressure, pulmonary arterial pressure, mean arterial pressure, capillary wedge pressure, systemic vascular resistance, cardiac output, mixed venous O 2  saturation, arterial O 2  saturation, blood pressure, heart rate, patient weight, and hematocrit.

RELATED APPLICATION

This application is a continuation, of application Ser. No. 08/478,946,filed Jun. 7, 1995 abandoned, which is a continuation-in-partapplication of U.S. patent application Ser. No. 08/299,899, filed Sep.1, 1994, abandonded which is a continuation of patent application Ser.No. 08/062,928, filed May 17, 1993, now U.S. Pat. No. 5,344,568 whichissued Sep. 6, 1994, which is a continuation of patent application Ser.No. 07/775,183, filed Oct. 11, 1991, now U.S. Pat. No. 5,211,849 whichissued May 18, 1993.

FIELD OF THE INVENTION

The present invention is directed to a system and method of bloodfiltration, and more particularly a continuous system and method for theregulation of the rate of filtration of fluid and/or soluble waste fromthe blood of a patient based on one or more monitored patientparameters.

BACKGROUND OF THE INVENTION

For various reasons, including illness, injury or surgery, patients mayrequire replacement or supplementation of their natural renal functionin order to remove excess fluid or fluids containing dissolved wasteproducts from their blood. Several procedures known for this purpose aredialysis, hemodialysis, hemofiltration, hemodiafiltration andultrafiltration; another related procedure is plasmapheresis. Thespecific procedure employed depends upon the needs of the particularpatient. For example, dialysis is used to remove soluble waste andsolvent from blood; hemofiltration is used to remove plasma water fromblood; hemodiafiltration is used to remove both unwanted solute (solublewaste) and plasma water from blood; ultrafiltration is a species ofhemofiltration; and plasmapheresis is used to remove blood plasma bymeans of a plasmapheresis filter. Because the replacement of renalfunction may affect nutrition, erythropoiesis, calcium-phosphorusbalance and solvent and solute clearance from the patient, it isimperative that there be accurate control of the procedure utilized. Theaccurate control of the rate of removal of intravascular fluid volume isalso important to maintain proper fluid balance in the patient andprevent hypotension.

Various systems have been proposed to monitor and control renalreplacement procedures. For example, U.S. Pat. No. 4,132,644 discloses adialysis system in which the weight of dialyzing liquid in a closedliquid container is indicated by a scale. After the dialyzing liquidflows through the dialyzer, the spent liquid is returned to the samecontainer and the weight is again indicated. Since the containerreceives the original dialyzing liquid plus ultrafiltrate, the amount ofultrafiltrate removed from the patient is equal to the increase in totalweight in the container. This system is not driven by a weight measuringdevice and does not offer precise control of the amount of liquids usedin the procedure.

U.S. Pat. No. 4,204,957 discloses an artificial kidney system whichutilizes weight measurement to control the supply of substitute fluid toa patient. In this system, the patient's blood is pumped through afilter and the filtrate from the blood is discharged to a measuringvessel associated with a weighing device. A second measuring vesselcontaining substitute fluid is associated with a second weighing deviceand is connected to the purified blood line. By means of a pump, thesubstitute fluid and the purified blood are pumped back to the patient.The first and second weighing devices are coupled to one another by ameasuring system in such a way that a fixed proportion of substitute issupplied to the purified blood stream from the second measuring vesseldepending an the weight of the filtrate received in the first measuringvessel. This system does not utilize circulating dialysate fluid in theblood filtration.

U.S. Pat. No. 4,767,399 discloses a system for performing continuousarteriovenous hemofiltration (CAVH). The disclosed system relies uponutilizing a volumetric pump to withdraw a desired amount of fluid fromthe patient's blood and return a selected amount of fluid volume to thepatient.

U.S. Pat. No. 4,923,598 discloses an apparatus for hemodialysis andhemofiltration which comprises an extracorporeal blood circuit includinga dialyzer and/or filter arrangement. The system determines fluidwithdrawal per unit time and total amount of fluid withdrawn byutilizing flow sensors in conjunction with an evaluating unit locatedupstream and downstream of the dialyzer or filter arrangement in theblood circuit.

U.S. Pat. No. 4,728,433 discloses a system for regulatingultrafiltration by differential weighing. The system includes adifferential weighing receptacle having an inlet chamber and an outletchamber which allows a fixed amount of fresh dialysate, by weight, toflow through the hemodialyzer. This system operates in a sequence ofweighing cycles during which the amount of ultrafiltrate removed fromthe blood may be calculated. Additionally, the ultrafiltration rate foreach weighing cycle may be calculated. This system provides a mechanismfor determining and regulating the amount of ultrafiltrate removed fromthe blood while delivering dialysate to the patient in alternating filland drain cycles of the inlet and outlet chambers of the differentialweighing receptacle.

The need exists for a multipurpose renal functionreplacement/supplementation system which is accurate, reliable, capableof continuous, long-term operation, and which can be used effectively onadult, pediatric and neonatal patients.

SUMMARY OF THE INVENTION

The present invention is directed to a multipurpose system and methodfor removal of fluid and/or soluble waste from the blood of a patient:ultrafiltration only, hemodiafiltration, hemodiafiltration andultrafiltration, and plasmapheresis with or without fluid replacement.The system and method of the present invention can provide reliable,long term operation (5-10 days) with a great degree of accuracy (on theorder of +−2 grams regardless of the total volume of fluid passingthrough the system). The system and method of the invention areadvantageous because of the multipurpose nature thereof, therepeatability and accuracy of the processes, and the simultaneous,continuous flow of fluids in an extracorporeal blood circuit, whilebeing equally applicable to adult, pediatric and neonatal patients.

As used herein the term “hemofiltration” is to be broadly construed toinclude hemodialysis, hemofiltration, hemodiafiltration, ultrafiltrationand plasmapheresis processes. As used herein, the term “infusate” isdefined to include dialysate fluid or any other replacement fluids whichmay be supplied to the patient as a part of the hemofiltrationprocedures.

In a preferred embodiment, the system of the present invention includesa hemofilter, a blood pump for pumping blood from a patient through thehemofilter and back to the patient, and suitable tubing for carrying thepumped blood to and from the patent. The system further includes a firstreservoir for maintaining a supply of infusate, a first weighing meansfor continuously monitoring the weight of the infusate and generatingweight data signals correlated to the monitored weight, and a first pumpfor pumping the infusate from the first reservoir to the hemofilter orappropriate blood tubing access port. A second reservoir receivesdrained fluid (e.g., spent infusate or ultrafiltrate, including thefluids and solutes removed from the blood) from the hemofilter, and asecond weighing means monitors the weight of the drained fluid andgenerates weight data signals correlated to the monitored weight. Asecond pump pumps the drained fluid from the hemofilter to the secondreservoir. The system also includes a computerized controller operablyconnected to the blood pump, the infusate pump, the drain pump and thefirst and second weighing means.

The controller periodically, but on an ongoing basis during thetreatment, interrogates at predetermined intervals the weight datasignals that are continuously generated by the first and second weighingmeans and is designed to determine therefrom the weight of infusate anddrained fluid in the first and second reservoirs at the predeterminedintervals. The rate of fluid withdrawal from the blood is alsodetermined. The controller compares the infusate and drained fluidweights to corresponding predetermined computed weights in the memory ofthe controller, and, when necessary, the controller generates controlsignals which automatically adjust the pumping rates of the infusate anddrained fluid pumps in order to achieve a preselected amount of fluidremoval from the patient's blood. Additionally, the controller isprogrammed to operate the infusate and drained fluid pumps only when theblood pump is operating. Furthermore, the blood pump is operablyconnected to and is responsive to control signals generated by thecontroller in response to or independent of the weight data signals tovary the flow rate of the blood through the hemofilter as required toachieve the desired level of fluid removal from the blood.

In an alternative embodiment, the computer controller is, by initialselection of the operator, interfaced with one or more of the variousmonitoring systems that are operably connected to the patient. Thesemonitoring systems, which are well known in the art, generate and outputdata signals corresponding to the monitored patient parameters, and thecomputer controller receives such data signals. During thehemofiltration operation, the interfaced parameters are constantlymonitored; however, the controller only responds to specific parameterdata that corresponds to the patient parameters selected by theoperator. The patient parameters which may be monitored and interfacedwith the computer controller include the following: arterial pressure,central venous pressure, pulmonary arterial pressure, mean arterialpressure, capillary wedge pressure, systemic vascular resistance,cardiac output, O₂ saturation (mixed venous or arterial), bloodpressure, heart rate, patient weight, external infusion rates, andhematocrit. Numerous of these parameters may be monitored andcorresponding output data signals generated in known manner utilizing anindwelling intravenous or intra-arterial catheter. The remainingparameters are monitored and data signals are generated by means wellknown in the art. The operator will select one or more of the aboveparameters to interface with the controller which will thenperiodically, but on an ongoing basis during treatment, interrogate atpredetermined intervals the parameter data signals that are continuouslygenerated by the interfaced monitoring system(s). The controller thenevaluates the parameter data and in response thereto, when necessary,the controller generates control signals which automatically adjust thepumping rates of the infusate, drained fluid and blood pumps so as toachieve a preselected amount of fluid removal from the patient's blood.

It will be appreciated that the system of the present invention mayutilize a combination of monitoring and responding to the infusate anddrained fluid weight data signals, as described in connection with thefirst embodiment hereinabove, along with one or more of the otherpatient parameters interfaced to the controller.

By way of specific examples, in connection with monitoring the patient'sweight, the computer controller may be interfaced with a bed scale whichprovides continuous values for the patient's weight. In response to theoverall patient weight data signals, the computer controller may controlthe infusate and/or drained fluid pumps to achieve a predesignedprotocol for decreasing or increasing the patient's weight over time.The change in patient's weight (by increase or decrease) can beaccomplished in either a linear or non-linear (such as curvilinear)manner with respect to time by appropriate pump control. Similarly, thecomputer may be interfaced with a continuous read-out device of thepatient's O₂ saturation and the controller will receive, evaluate andrespond to the O₂ saturation data by controlling the infusate, drainedfluid and blood pumping rates accordingly.

In connection with all of the above-described monitored parameters, thecomputer controller will receive data signals corresponding and relatingto each particular selected parameter from an appropriate signalgenerating device or source operably connected to the patient. Thecontroller will then, after periodic interrogation, compare theinterrogated values with predetermined desired values and willautomatically make the appropriate, predetermined changes in theinfusate, drained fluid and blood pumping rates in response to themonitored signals. Furthermore, more than one of the above-referencedparameters can be continuously monitored simultaneously and the computermay be programmed with a hierarchy to consider one or more specificparameters rather than others and will respond with the appropriate anddesired adjustments in infusate, drained fluid and blood pumping ratesbased on those selected parameters.

The computer controller is designed and programmed to adjust the pumpingrates (pump speed) of the infusate, drained fluid and blood pumps so asto provide a linear response or a non-linear (curvilinear) response tothe observed changes in the selected monitored parameters. In thisregard, “linear” is defined to mean a fixed, non-exponential change, and“non-linear” or “curvilinear” means anything other than linear. Theselection of linear versus non-linear response profile is made by theoperator of the system depending on the needs of the patient. Forexample, in certain situations it may be desirable to have an initiallyfast fluid removal rate that decreases over time. In that case acurvilinear or exponential response would be utilized. In othercircumstances, consistent or constant fluid removal over time isdesired, and so a linear response profile is selected. It is furthercontemplated that at the election of the operator the computercontroller may combine linear and curvilinear response signals so as totailor the pump rates to achieve a desired response profile. Forexample, a non-linear initial response period for fast initial fluidremoval, followed by a linear response period for ongoing fluid removalat a consistent rate.

In yet another alternative embodiment, the computer controller receivesdata signals from one or more patient infusion pumps that are otherwiseindependent of the hemofiltration system. These infusion pumps are usedfor infusion to the patient of intravenous fluids, medications,parenteral nutrition and/or blood products. By monitoring the dataoutput from the independent infusion pumps, the extraneous total fluidvolume per unit time may be ascertained. The controller will then, asrequired, change the pumping rates of the system infusate, drained fluidand blood pumps, as necessary, so as to alter the ultrafiltration rateand/or infusate fluid rate automatically in response to changes inintravenous fluid therapy. This facilitates independent patientmanagement while hemofiltration is being performed. Proper coordinationof the controller with the independent infusion pumps allows the desiredor targeted fluid removal goals by hemofiltration to be achievedautomatically in concordance with ongoing intravenous fluid therapy.

In a preferred embodiment of the method of the present invention, bloodfrom a patient is pumped through a hemofilter and a supply of infusate,which is maintained in a first reservoir, is pumped from the firstreservoir through the hemofilter, countercurrent to the blood. Theweight of infusate in the first reservoir is continuously monitored anddata signals correlated to that weight are generated. Drained fluid(e.g., spent infusate) is pumped from the hemofilter and is received ina second reservoir. The weight of the drained fluid in the secondreservoir is continuously monitored and weight data signals correlatedthereto are generated. The signals correlated to the weight of infusateand drained fluid are interrogated at regular intervals (for exampleevery minute) by a system controller and are compared to correspondingpredetermined computed weights in the memory of the controller. Thecontroller determines the amount and rate of fluid withdrawal from thepatient's blood. If those values differ from preselected, preprogrammeddesired values, the controller generates control signals whichindependently adjust the pumping rates of the infusate and drained fluidpumps so as to achieve the desired amount of fluid removal. The controlsignals may also control the blood pumping rate.

In an alternative embodiment of the method of the present invention,independent of or in addition to the infusate and drained fluid weightmonitoring and pump control, the computer controller may be interfacedwith one or more of the previously discussed monitoring systems. In thisembodiment, the controller will receive, evaluate and respond to theselected patient parameter data by generating appropriate, responsivecontrol signals by which the infusate, drained fluid and blood pumpingrates are controlled to achieve the desired amount of fluid removal.This may be accomplished in combination with or independent of theinfusate and drained fluid weight monitoring.

The advantages of the system and method of the present invention areachieved at least in part due to the continuous monitoring and periodicinterrogation of the fluid weights, and other selected patientparameters, and the adjustment of fluid pumping rates in responsethereto, including the blood pumping rate, so as to achieve ideal ornearly ideal fluid removal and replacement if necessary from a patient'sblood. Further features and advantages of the system and apparatus ofthe present invention will become apparent with reference to the Figureand the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic representation of one embodiment of the systemof the present invention; a variation is shown in phantom.

FIG. 2 is a diagrammatic representation of an alternative embodiment ofthe system of the present invention.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a diagrammatic representation of a preferred embodiment ofthe system of the present invention. The portion of FIG. 1 shown inphantom represents an alternative embodiment of the present inventionwhich will be described hereinbelow. Hemofiltration system 10 isoperated and controlled by a suitable controller designated generally as12. Controller 12 may be a programmable computer such as a COMPAQ 386/Shaving a display 13 and is operably connected to various components ofhemofiltration system 10, as will be described in greater detailhereinafter.

In operation, blood is pumped from a patient (not shown), which may bean adult, pediatric or neonatal patient, through a suitable catheter(not shown) and input tubing 14 by means of a blood pump 16. Blood pump16, which is preferably of the roller type, is operably connected tocontroller 12 by line 18. One suitable blood pump is the RS-7800Minipump manufactured by Renal Systems, Minneapolis, Minn. Input tubing14 through which the patient's blood is pumped preferably includes apressure transducer 20 upstream of pump 16. Pressure transducer 20 isoperably connected to controller 12 via line 21. Means are includeddownstream of blood pump 16 for accessing input tubing 14 to enable theinjection or infusion of desired fluids, including medications andanticlotting compounds such as heparin, into the patient's blood. Theinjection or infusion of such fluids to the blood may be accomplished inany suitable manner; FIG. 1 shows diagrammatically a syringe and tubearrangement 22, but it will be appreciated that other means could beemployed for the same purpose.

The patient's blood is pumped through hemofilter 24 by blood pump 16.Filters of the type suitable for use in the system of the presentinvention are readily available; one example of a suitable hemofilter isthe Diafilter manufactured by AMICON, Denvers, Mass. Where the presentsystem is used to perform plasmapheresis, a suitable plasmapheresisfilter such as the Plasmaflo manufactured by Parker Hannifin, Irvine,Calif. can be employed.

Input tubing 14 includes a second pressure transducer 26 slightlyupstream of hemofilter 24. Pressure transducer 26 is operably connectedto controller 12 via line 28. The patient's blood exits hemofilter 24,passes through output tubing 30 and is returned to the patient via anysuitable means such as a venous catheter arrangement (not shown). Outputtubing 30 preferably includes a suitable blood flow detector 31 whichverifies that there is blood flow in the system and an air bubble/foamcontrol device such as air bubble clamp 32 to prevent the passage of airbubbles to the patient. Blood flow detector 31 and air bubble clamp 32may be operably connected (not shown) to controller 12 or directly tothe pumps to interlock all pumps upon detection of any air bubbles inthe blood or upon the cessation of blood flow. A suitable foam-bubbledetector is the RS-3220A manufactured by Renal Systems. Output tubing 30also preferably includes a pressure transducer 34 immediately downstreamof hemofilter 24. Pressure transducer 34 is operably connected tocontroller 12 via line 36.

A first reservoir 50 maintains a supply of suitable dialysate or otherfluid, referred to herein generally as infusate 52. Theinfusate-containing reservoir 50 is supported by a weighing device suchas electronic scale 54 which is operably connected to controller 12 vialine 56. Infusate 52 is pumped from reservoir 50 via tubing 58 by meansof infusate pump 60, which is preferably of the roller variety. Asuitable pump for this purpose is a 3½ Roller Pump manufactured byPEMCO, Cleveland, Ohio. Infusate pump 60 is operably connected tocontroller 12 via line 62 and pumps infusate 52 through hemofilter 24countercurrent to the blood pumped therethrough. In accordance withknown principles, infusate 52 may extract certain components (fluidsand/or soluble waste) from the blood passing through hemofilter 24. Thefluid drained from hemofilter 24 includes spent infusate and thecomponents removed from the blood, which are referred to herein asdrained fluid 76. In an alternative embodiment wherein system 10 is usedas a fluid or plasma replacement system, e.g., to performplasmapheresis, the infusate (which may be blood plasma) from reservoir50 is pumped via tubing 59 (shown in phantom) to blood output tubing 30,thereby replacing the fluid volume removed from the blood. In thisembodiment, the drained fluid 76 from hemofilter or plasmapheresisfilter 24 does not include any spent infusate since the infusate ispumped directly to blood output tubing 30 and supplied to the patient.

The drained fluid 76 is pumped from hemofilter 24 through outlet tubing64 by means of drain pump 66, which is preferably a roller-type pump,and may be the same as infusate pump 60. Drain pump 66 is operablyconnected to controller 12 via line 68. Output tubing 64 preferablyincludes a pressure transducer 70 downstream of hemofilter 24, butupstream of drain pump 66. Pressure transducer 70 is operably connectedto controller 12 via line 72. Output tubing 64 also preferably includesa blood leak detector 67 which detects the presence of blood in thedrained fluid 76, as may occur if hemofilter 24 ruptures. A suitableblood leak detector is sold by COBE, Lakewood, Colo. as model 500247000.Blood leak detector 67 may be operably connected (not shown) tocontroller 12 or directly to the pumps to interlock all pumps upon thedetection of blood in the drained fluid. Drained fluid 76 pumped fromhemofilter 24 is pumped into a second reservoir 74 which collects thedrained fluid. Second reservoir 74 is supported by a weighing devicesuch as electronic scale 78, which is operably connected to controller12 via line 80.

Scales 54 and 78, which may be model 140 CP sold by SETRA of Acton,Mass. continuously generate weight data signals correlated to the weightof infusate and drained fluid contained in reservoirs 50 and 74,respectively. Those weight data signals are continuously fed tocontroller 12, to which the scales are linked through an RS-232interface. It will be appreciated that a single scale could be utilizedin place of the two scales whereby the weight differential betweenreservoir 50 and 74 is monitored and a corresponding data signal isgenerated. Pressure transducers 20, 26, 34 and 70 all continuouslymeasure the pressure at their respective locations in hemofiltrationsystem 10 and generate pressure data signals correlated thereto whichare fed to controller 12. A suitable type of pressure transducer ismodel number 042-904-10 sold by COBE of Lakewood, Colo. When certainpredetermined alarm or danger conditions exist in the system 10, asrepresented by the pressure data signals, the controller will eitheradjust the infusate, drained fluid, or blood pumping rate, or acombination thereof, or will shut the system down entirely.

Controller 12 is preferably a programmable computer that is capable ofsending and receiving signals from auxiliary equipment includingpressure transducers 20, 26, 34 and 70, first and second scales 54 and78, respectively, and blood pump 16, infusate pump 60, and drain pump66. In operation, controller 12 interrogates, at regular intervals, theweight data signals generated by first and second scales 54 and 78. Fromthese signals, controller 12 determines the weight of infusate anddrained fluid in the first and second reservoirs 50 and 74 at that pointin time, and compares those weights to corresponding predeterminedcomputed weights which have been programmed into and are stored bycontroller 12. By monitoring the weight of infusate in reservoir 50 andthe weight of drained fluid in reservoir 74 at regular intervals, therate of change of those weights and the rate of hemofiltration can becalculated by the computer portion of controller 12. When the weightsdeviate from the predetermined computed weights and/or the rate ofhemofiltration deviates from a preselected, preprogrammed desired rate,controller 12 generates control signals which control or adjust therates at which blood pump 16, infusate pump 60 and drain pump 66 areoperated, as necessary, to adjust the hemofiltration rate to the desiredrate, or to stop the pumps when preselected limits have been reached.This is accomplished in a continuous manner; i.e., continuous weightdata signal generation, periodic interrogation of those weight datasignals and computation of the required weight and/or rate information,comparison to predetermined computed values and automatic adjustment ofthe pumping rates of the pumps, as necessary, to achieve the desiredamount and/or rate of hemofiltration.

Controller 12 is programmed so that infusate pump 60 and drain pump 66are operated only when blood pump 16 is being operated. In the case whenultrafiltration is being performed, the pumping rate of drain pump 66must equal the pumping rate of infusate pump 60 plus the desiredultrafiltration rate.

Controller 12 continuously receives pressure data signals from pressuretransducers 20, 26, 34 and 70 and is programmed to generate alarmsignals when high and low pressure limits are exceeded at any of themonitored locations. Furthermore, an alarm signal is generated when thepressure differential across hemofilter 24 exceeds a predetermined upperlimit, as monitored specifically by pressure transducers 26, 34 and 70.Additionally, controller 12 may stop the pumps when preselected pressurelimits (high or low) are exceeded, as for example may occur if thesystem tubing becomes occluded or ruptures or if pump occlusion occurs.Finally, controller 12 may signal when the infusate level in reservoir50 reaches a predetermined lower limit and when the drained fluid levelin reservoir 76 reaches a predetermined upper limit. Hemofiltrationsystem 10 may also include suitable blood warmer and infusate warmerdevices (not shown) to adjust and/or maintain the blood and infusatetemperatures at desired levels. Such devices may also generate alarmsignals when the fluid temperatures are outside of preselected limits.

Display 13 offers updated display of measured and computed parameterssuch as pressures, pressure differentials, temperatures, flow rates andamounts of infusate, drain and ultrafiltration, and alarm conditions.Controller 12 generates both visual and audible alarms and all the pumpsare interlocked to prevent operation thereof under alarm conditions.Users have the option of disabling or unabling the alarms (the audiblepart of the alarm and its interlock with the pumps) to perform aprocedure under close supervision. A printer (not shown) is operablyconnected (not shown) to controller 12 to generate a hard copy ofprocedural data currently displayed or stored at regular intervals, atthe completion of a procedure or at any desired time.

Hemofiltration system 10 can be operated in one of two modes: 1) amanual mode wherein the pumping rates of blood pump 16, infusate pump 60and drain pump 66 are provided by controller 12 when fixed voltages areapplied; and 2) an automatic mode wherein the pumps are controlled bycontroller 12 when the desired hemofiltration amount or rate has beenprogrammed into the controller. The automatic mode allows the system tobe paused and later continued without losing previously measured andcomputed data.

FIG. 2 shows a diagrammatic representation of several alternativeembodiments of the system 10 of the present invention. Because of thecommonality of many of the system components in FIG. 2 vis-a-vis thesystem depicted in FIG. 1, like reference numerals are intended toindicate like components. Furthermore, the system components in FIGS. 2operate in the same manner as the corresponding system components shownin FIG. 1 and described hereinabove.

The system of FIG. 2 further includes interfaces between controller 12and monitoring systems which generate parameter data signalscorresponding to selected patient parameters such as O₂ saturation 100,hematocrit 110, patient blood pressure 120, patient heart rate 130 andnumerous other patient parameters (designated generally as 140), whichother parameters may be one or more of the following: arterial pressure,central venous pressure, pulmonary arterial pressure, mean arterialpressure, capillary wedge pressure, systemic vascular resistance,cardiac output, and patient weight. While the O₂ saturation sensor 100and hematocrit sensor 110 are shown as being connected to the patientblood line 14, these parameters can also be monitored by meansassociated directly with the patient rather than via blood tubing 14. Infact, whereas venous O₂ saturation could be measured as indicated,arterial O₂ saturation would require the monitor to be locatedelsewhere. The overall patient weight parameter can be monitoredutilizing a standard patient bed scale (not shown) as is well known inthe art.

During the hemofiltration operation, one or more of the various patientparameters will be monitored continuously and the controller will, atthe selection of the operator, be responsive to selected parameter datasupplied to the controller. The parameter data may be evaluated andresponded to by the controller independent of the infusate and drainedfluid weight data signals; i.e., the system may operate and respondbased on one or more of the selected parameters and not the weight datasignals; or the system may respond to a combination of the weight datasignals and one or more selected specific parameters.

One or more independent patient infusion pumps 150 may be interfacedwith computer controller 12 to supply data signals correlated to theinfusion to the patient of intravenous fluids, medications, parenteralnutrition and/or blood products. The controller 12 may evaluate thisdata and make modifications to the infusate, drained fluid and bloodpumping rates so as to compensate for the extraneous fluid beingdelivered to the patient by means of the infusion pumps. In this regard,the overall fluid balance in the patient can be managed concurrent witha hemofiltration operation.

It will be appreciated by persons skilled in the art that variousmodifications can be made to the systems and methods of the presentinvention without departing from the scope thereof which is defined bythe appended claims.

What is claimed is:
 1. Continuous hemofiltration system for removal offluid from the blood of a patient, comprising: a hemofilter; a firstpump for pumping blood from a patient through said hemofilter and backto the patient; a first reservoir for maintaining a supply of infusate;a first scale for monitoring the weight of the infusate and generatingweight data signals correlated thereto; a second pump for pumping theinfusate from said first reservoir to said hemofilter; a secondreservoir for receiving drained fluid from said hemofilter; a secondscale for monitoring the weight of the drained fluid and generatingweight data signals correlated thereto; a third pump for pumping thedrained fluid from said hemofilter to said second reservoir; at leastone monitor for monitoring a predetermined patient parameter selectedfrom the group consisting of arterial pressure, central venous pressure,pulmonary arterial pressure, mean arterial pressure, capillary wedgepressure, systemic vascular resistance, cardiac output, mixed venous O₂saturation, arterial O₂ saturation, blood pressure, heart rate, patientweight, and hematocrit, and generating parameter data signals correlatedthereto; and a computer controller operably connected to said first pumpand to each of said second and third pumps, said first and second scalesand said at least one patient parameter monitor; said controllerreceiving said weight data signals generated by said first and secondscales and said parameter data signals generated by said at least oneparameter monitor, determining from said weight data signals the weightof infusate and drained fluid in said first and second reservoirs,respectively, at regular intervals, comparing those weights tocorresponding predetermined computed weights, determining from saidparameter data signals the corresponding patient parameter data,comparing the parameter data to corresponding predetermined data, andgenerating control signals in response to said weight data and parameterdata signals, whereby said control signals adjust continuously andautomatically as necessary on an ongoing basis during hemofiltration therates of pumping one or more of the infusate, drained fluid and bloodwhile the pumps are pumping during hemofiltration so as to remove apreselected amount of fluid from the blood over a preselected timeperiod.
 2. A hemofiltration system according to claim 1 furthercomprising: an interface with one or more infusion pumps supplying fluidto the patient, said controller receiving infusion data signals from theone or more infusion pumps.
 3. Continuous hemofiltration system forremoval of fluid from the blood of a patient, comprising: a hemofilter;a first pump for pumping blood through said hemofilter and back to thepatient; a supply of infusate; a second pump for pumping the infusate tosaid hemofilter; a receptacle for receiving drained fluid from saidhemofilter; a third pump for pumping the drained fluid from saidhemofilter to said receptacle; at least one monitor for monitoring apredetermined patient parameter selected from the group consisting ofarterial pressure, central venous pressure, pulmonary arterial pressure,mean arterial pressure, capillary wedge pressure, systemic vascularresistance, cardiac output, mixed venous O₂ saturation, arterial O₂saturation, blood pressure, heart rate, patient weight, and hematocrit,and generating parameter data signals correlated thereto; and a computercontroller operably connected to said first pump, said second and thirdpumps, and said at least one patient parameter monitor; said controllerreceiving said parameter data signals generated by said at least oneparameter monitor, determining from said parameter data signals thecorresponding patient parameter data, comparing the parameter data tocorresponding predetermined data, and generating control signals inresponse to said parameter data signals, whereby said control signalsadjust continuously and automatically as necessary on an ongoing basisduring hemofiltration the rates of pumping one or more of the infusate,drained fluid and blood while the respective pumps are pumping duringhemofiltration so as to remove a preselected amount of fluid from theblood over a preselected time period.
 4. Hemofiltration method forremoval of fluid from the blood of a patient, comprising: pumping bloodfrom a patient through a hemofilter and back to the patient; maintaininga supply of infusate in a first reservoir; pumping the infusate to thehemofilter; monitoring the weight of the infusate and generating weightdata signals correlated thereto; pumping drained fluid from thehemofilter into a second reservoir; monitoring the weight of the drainedfluid and generating weight data signals correlated thereto; monitoringat least one predetermined patient parameter selected from the groupconsisting of arterial pressure, central venous pressure, pulmonaryarterial pressure, mean arterial pressure, capillary wedge pressure,systemic vascular resistance, cardiac output, mixed venous O₂saturation, arterial O₂ saturation, blood pressure, heart rate, patientweight, and hematocrit, and generating parameter data signals correlatedthereto; and controlling the pumping rates of the blood, infusate anddrained fluid by means of a programmed computer, said computer beingresponsive to the infusate and drained fluid weight data signals and tosaid parameter data signals, said computer receiving said weight datasignals and said parameter data signals, determining from said weightdata signals, at regular intervals, the weight of infusate in the firstreservoir and the weight of drained fluid in the second reservoir,comparing those weights to corresponding predetermined computer weights,determining from said parameter data signals the corresponding patientparameter data, comparing the parameter data to correspondingpredetermined data, and generating control signals in response to saidweight data and parameter data signals, whereby said control signalsadjust continuously and automatically as necessary on an ongoing basisduring hemofiltration the rates of pumping one or more of the infusate,drained fluid and blood while the respective pumps are pumping duringhemofiltration so as to remove a preselected amount of fluid from theblood.
 5. A hemofiltration method according to claim 4 furthercomprising: interfacing said computer with one or more infusion pumpssupplying fluid to the patient, said computer receiving infusion datasignals from the one or more infusion pumps.
 6. The hemofiltrationmethod of claim 4 wherein said control signals adjust the pumping ratesof one or more of the infusate, drained fluid and blood pumps such thatthe fluid removed from the patient's blood is removed in a linearprofile over time.
 7. The hemofiltration method of claim 4 wherein saidcontrol signals adjust the pumping rates of one or more of the infusate,drained fluid and blood pumps such that the fluid removed from thepatient's blood is removed in a non-linear profile over time. 8.Hemofiltration method for removal of fluid from the blood of a patient,comprising: pumping blood from a patient through a hemofilter and backto the patient; maintaining a supply of infusate; pumping the infusateto the hemofilter; pumping drained fluid from the hemofilter into areservoir; monitoring at least one predetermined patient parameterselected from the group consisting of arterial pressure, central venouspressure, pulmonary arterial pressure, mean arterial pressure, capillarywedge pressure, systemic vascular resistance, cardiac output, mixedvenous O₂ saturation, arterial O₂ saturation, blood pressure, heartrate, patient weight, and hematocrit, and generating parameter datasignals correlated thereto; and controlling the pumping rates of theblood, infusate and drained fluid by means of a programmed computer,said computer being responsive to said parameter data signals, saidcomputer receiving said parameter data signals, determining from saidparameter data signals the corresponding patient parameter data,comparing the parameter data to corresponding predetermined data, andgenerating control signals in response to said parameter data signals,whereby said control signals adjust continuously and automatically asnecessary on an ongoing basis during hemofiltration the rates of pumpingone or more of the infusate, drained fluid and blood while therespective pumps are pumping during hemofiltration so as to remove apreselected amount of fluid from the blood.